Conversion of ethers

ABSTRACT

Process of converting aliphatic ethers, particularly alkyl ethers, to other desirable products by contacting such with a crystalline aluminosilicate molecular sieve catalyst having a constraint index of about 1 to 12 and a silica to alumina ratio of at least about 12 at elevated temperature. The catalyst preferably has a crystal density in the hydrogen form of not substantially below about 1.6 grams per cubic centimeter. Products produced by such conversion vary with temperature, with conversion to aromatic rings and substituted aromatic rings predominating at higher temperatures of about 500* to 1000*F.

United States Patent Chang et al. 5] July 8, 1975 CONVERSION OF ETHERS3,751,504 8/1973 Keown et a1. 260/672 T [75] lnvemorsl Clarence Changprmceton; 3,755,483 8/1973 260/671 5 William H. Lang, Pennington, bothof N.J.; Anthony J. Silvestri, Morrisville, Pa.

Assignee: Mobil Oil Corporation, New York,

Filed: Aug. 9, 1973 Appl. No.: 387,222

[52] US. Cl 260/668 R; 208/135; 260/673; 208/141; 260/673.5; 260/676 R;260/682 [51] Int. Cl. C07c l/20 [58] Field of Search... 208/135, 141,668 R, 449 R, 208/449 M, 449 L; 260/449.5, 671 R, 671 C, 671 M, 673,673.5, 682; 252/455 Z [56] References Cited UNITED STATES PATENTS3,728,408 4/1973 Tobias 260/668 C Primary Examiner-C. Davis Attorney,Agent, or Firm-Charles A Huggett; Michael G. Gilman [5 7] ABSTRACTProcess of converting aliphatic ethers, particularly alkyl ethers, toother desirable products by contacting such with a crystallinealuminosilicate molecular sieve catalyst having a constraint index ofabout 1 to 12 and a silica to alumina ratio of at least about 12 atelevated temperature. The catalyst preferably has a crystal density inthe hydrogen form of not substantially below about 1.6 grams per cubiccentimeter. Products produced by such conversion vary with temperature,with conversion to aromatic rings and substituted aromatic ringspredominating at higher temperatures of about 500 to 1000F.

9 Claims, No Drawings CONVERSION OF ETHERS This invention relates toconversion of certain organic compounds to other, more complicatedorganic compounds. Thisrecently discovered novel class of zeolites hassome unusual properties. These catalysts induce profound transformationsof aliphatic hydrocarbons to aromatic hydrocarbons in commerciallydesirable yields. Although they have unusually low alumina contents,i.e. high silica to alumina ratios, they are very active even when thesilica to alumina ratio exceeds 30. The activity is surprising since thealumina in the zeolite framework is believed responsible for catalyticactivity. These catalysts retain their crystallinity for long periods inspite of the presence of steam at high temperature which inducesirreversible collapse of the framework of other zeolites, e.g. of the Xand A type. Furthermore, carbonaceous deposits, when formed, may beremoved by burning at higher than usual temperatures to restoreactivity.

An important characteristic of the crystal structure of this class ofzeolites is that it provides constrained access to, and egress from,this intracrystalline free space by virtue of having a pore dimensiongreater than about 5 Angstroms and pore windows of about a size such aswould be provided by lO-membered rings of oxygen atoms. It is to beunderstood, of course, that these rings are those formed by the regulardisposition of the tetrahedra making up the anionic framework of thecrystalline aluminosilicate, the oxygen atoms themselves being bonded tothe silicon or aluminum atoms at the centers of the tetrahedra. Briefly,the preferred type catalyst useful in this invention posess, incombination: a silica to alumina ratio of at least about 12; and astructure providing constrained access to the crystalline free space.

The silica to alumina ratio referred to may be determined byconventional analysis. This ratio is meant to represent, as closely aspossible, the ratio in the rigid anionic framework of the zeolitecrystal and to exclude aluminum in the binder or in cationic form withinthe "1 .1915 Although catalysts with a silica to alumina ratio of atleast 12 are useful, it is preferred to use catalysts having higherratios of at least about 30. Such catalysts, after activation, acquirean intracrystalline sorption capacity for normal hexane which is greaterthan that for water, i.e. they exhibit hydrophobic properties. It isbelieved that this hydrophobic character is advantageous in the presentinvention.

The type zeolites useful in this invention freely sorb normal hexane andhave a pore dimension greater than about 5 Angstroms. In addition, thestructure must provide constrained access to larger molecules. It issometimes possible to judge from a known crystal structure whether suchconstrained access exists. For example, if the only pore windows in acrystal are formed by eight membered rings of oxygen atoms, then accessto molecules of largercross-section than normal hexane isexcluded andthe zeolite is not of the desired type. Windows of lO-membered rings arepreferred, although excessive puckering or pore blockage may renderthese catalysts ineffective. Twelve-membered rings do not generallyappear to offer sufficient constraint to produce the advantageousconversions, although structures can be conceived, due to pore blockageor other cause, that may be operative.

Rather than attempt to judge from crystal structure whether or not acatalyst posesses the necessary constrained access, a simpledetermination of the constraint index may be made by passingcontinuously a mixture of equal weight of normal hexane and 3methylpentane over a small sample, approximately 1 gram or less, ofcatalyst at atmospheric pressure according to the following procedure. Asample of the catalyst, in the form of pellets or extrudate, is crushedto a particle size about that of coarse sand and mounted in a glasstube. Prior to testing, the catalyst is treated with a stream of air at1000F for at least 15 minutes.

The catalyst is then flushed with helium and the temperature adjustedbetween 550 and 950F to give an log (fraction of n-hexane remaining) log(fraction of 3-rnethylpentane remaining) Constraint Index The constraintindex approximates the ratio of the cracking rate constants for the twohydrocarbons. Catalysts suitable for the present invention are thosehaving a constraint index from 1.0 to 12.0, preferably 2.0 to 7.0.

The class of zeolites defined herein is exemplified by ZSM-5, ZSM-l l,ZSM-12, ZSM'-21,'TEA mordenite and other similar materials. Recentlyissued U.S. Pat. No. 3,702,886 describing and claiming ZSM-S isincorporated herein by reference.

ZSM-ll is more particularly described in U.S. Pat. No. 3,709,979, theentire contents of which are incorporated herein by reference.

ZSM-12 is more particularly described in West German OffenlagunschrifftNo. 2,213,109, the entire contents of which are incorporated herein byreference.

ZSM-21 is more particularly described in U.S. application, Ser. No.358,192, filed May 7, 1973, and now abandoned, the entire contents ofwhich are incorporated herein by reference.

TEA mordenite is more particularly described in U.S. application Ser.No. 130,442 filed Apr. 11, 1971, the entire contents of which areincorporated herein by reference.

The specific zeolites described, when prepared in the presence oforganic cations, are catalytically inactive, possibly because theintracrystalline free space is occupied by organic cations from theforming solution. They may be activated by heating in an inertatmosphere at 1000"} for 1 hour, for example, followed by .-baseexchangewithammonium salts followed by calcination at 1000F in air. Thepresence of organic cations in the forming solution may not beabsolutely essential to the formation of this type zeolite; however, thepresence of these cations does appear to favor the formation of thisspecial type of zeolite. More generally, it is desirable to activatethis type catalyst by base exchange with ammonium salts followed bycalcination in air at about lOF for from about 15 minutes to about 24hours.

Natural zeolites may sometimes be converted to this type zeolitecatalysts by various activation procedures and other treatments such asbase exchange, steaming, alumina extraction and calcination, incombinations. Natural minerals which may be so treated includeferrierite, brewsterite, stilbite, dachiardite, epistilbite, heulanditeand clinoptilolite. The preferred crystalline aluminosilicates areZSM-S, ZSM-l l, ZSM-l2, ZSM-2l and TEA mordenite, with ZSM-Sparticularly preferred.

The catalysts of this invention may be in the hydrogen form or they maybe base exchanged or impregnated to contain ammonium or a metal cationcomplement. It is desirable to calcine the catalyst after base exchange.The metal cations that may be present include any of the cations of themetals of Groups I through VIII of the periodic table. However, in thecase of Group IA metals, the cation content should in no case be solarge as to effectively inactivate the catalyst. For example, acompletely sodium exchanged H-ZSM- 5 is not operative in the presentinvention.

In a preferred aspect of this invention, the catalysts hereof areselected as those having a crystal density, in the dry hydrogen form, ofnot substantially below about 1.6 grams per cubic centimeter. It hasbeen found that zeolites which satisfy all three of these criteria aremost desired because they tend to maximize the production of gasolineboiling range hydrocarbon products. Therefore, the preferred catalystsof this invention are those having a constraint index as defined aboveof about 1 to 12, a silica to alumina ratio of at least about 12 and adried crystal density of not less than about 1.6 grams per cubiccentimeter. The dry density for known structures may be calculated fromthe number of silicon plus aluminum atoms per 1000 cubic Angstroms, asgiven, tag. on page 1 l of the article on Zeolite Structure by W. M.Meier. This paper, the entire contents of which are incorporated hereinby reference, is included in Proceedings of the Conference on MolecularSieves, London, April 1967, published by the Society of ChemicalIndustry, London, 1968. When the crystal structure is unknown, thecrystal framework density may be determined by classical pyknometertechniques. For example, it may be determined by immersing the dryhydrogen form of the zeolite in an organic solvent which is not sorbedby the crystal. It is possible that the unusual sustained activity andstability of this class of zeolites is associated with its high crystalanionic framework density of not less than about 1.6 grams per cubiccentimeter. This high density of course must be associated with arelatively small amount of free space within the crystal, which might beexpected to result in more stable structures. This free space, however,is important as the locus of catalytic activity.

A remarkable and unique attribute of this type of zeolite is its abilityto convert paraffinic hydrocarbons to aromatic hydrocarbons inexceptionally fine, commercially attractive yields by simply contactingsuch paraffins with such catalyst at high temperatures of about 800 tol500F and low space velocities of about 1 to 15 WHSV. ZSM-S type ofzeolite seems to exert little or no action upon aromatic rings presentin the feed to such process or formed in such process from the point ofview of destroying (cracking such rings. It does however have theability with or without the presence of a special hydrogen transferfunctionality and with or without the presence of added hydrogen in thereaction mixture, to cause paraffinic fragments, which presumably havebeen cracked from paraffinic feed components, to alkylate aromatic ringsat somewhat lower temperatures of up to about 800 to I0O0F. It appearsthat the operative ranges for alkylation and formation of new aromaticrings overlap but that the optimum ranges are distinct, aromatizationbeing at a higher temperature. The exact mechanisms for these catalyticfunctions are not fully known or completely understood.

It is generally known to those of routine skill in the crystallinezeolite art, that catalytic properties thereof are often diminished bycontact with steam. Increasing the steam pressure, temperature and/ortime of contact of the zeolite with the steam increases the diminutionof catalytic properties.

It is known that many acid catalysts are capable of assisting in thedehydration of ethers to olefins. In all or at least most of these priorprocesses, the dehydrated product had a longest carbon atom chain lengthwhich was not longer than the longest carbon atom chain length of thereactant. For the most part, such dehydration reactions did not produceproducts having a molecular weight in any given hydrocarbon portionwhich was higher than the molecular weight of a correspondinghydrocarbon portion of the ether reactant.

It is an object of this invention to provide a novel process forconverting aliphatic ethers to other valuable products, particularlyhigher hydrocarbons.

It is a further object of this invention to convert aliphatic ethers toolefins and/or aromatics in a very efficient manner.

It is still another object of this invention to provide a novel processfor converting ethers to products having a greater number of carbonatoms in a continuous hydrocarbon portion of the product than in ahydrocarbon portion of the feed.

In accord with and fulfilling these objects, one aspect of thisinvention lies in the discovery that aliphatic ethers are convertible toother organic chemical products, notably aromatic hydrocarbons, bycontacting such ethers with a crystalline aluminosilicate molecularsieve zeolite having a silica to alumina ratio of at least about 12 anda constraint index of about I to 12 at elevated temperatures, preferablyabout 500 to 1000F a pressure of about atmospheric to 3000 psig, a spacevelocity of about 0.5 to 1000 WHSV in the presence or absence of addedhydrogen. The catalyst may be the zeolite alone or in a suitable matrix.The zeolite preferably has a crystal density in the hydrogen form of notsubstantially below about 1.6 grams per cubic centimeter. The etherreactant is preferably one or more alkyl ethers having 1 to 8 carbonatoms in the longest hydrocarbon constituent thereof. Mixed ethers aresuitable.

According to this invention, the reactive feed to the process hereof iscritically defined as consisting essentially of lower aliphatic ethercompounds. This feed definition is specifically intended to distinguishfrom feeds used in alkylation reactions catalyzed by this type ofsynthetic aluminosilicate molecular sieve. In such alkylation reactions,which are considered to be the invention of other than the instantapplicants, alkylating moieties, which may be ethers and/or othercompounds, are reacted with the preformed and co-fed aromatic moieties.In other words, alkylation requires the co-feeding of aromatic moietiesand alkylating moieties such as ethers. The instant process is to bedistinguished in that it does not require or desire the cofeeding ofpreformed aromatic moieties.

In this regard, two very important points must be emphasized: In thefirst place, it has now been discovered that the presence of preformedaromatic moieties as a co-feed to this reaction does not negate thearomatization conversion of the reactants designated above as the feedto the instant process; In the second place, new aromatic moietiescreated from the reactants hereof by the conversion process of thisinvention are themselves sometimes alkylated under these processingconditions by the alkylating action of the ether and/or one or moreintermediate moiety formed in the reaction being undergone. The processof this invention must therefore be distinguished from an alkylatingreaction per se carried out with the same catalyst and underco-extensive reaction conditions.

In its broadest aspects, this invention envisions a process forcondensing certain feed materials and growing the products thus formedinto significantly different chemical moieties. The commercially mostimportant aspect of this invention appears to be the conversion of loweralkyl ethers to aromatic compounds as aforesaid. However, as an adjunctto this conversion, the reaction can be carried out under differentconditions but with the same catalyst to produce somewhat differentchemical values. For example, lower alkyl ethers can be converted toolefins at somewhat lower temperatures and generally less severeoperating conditions than those which result in a predominantly aromaticproduct.

While at first glance the formation of olefins by contacting ethers withan acidic zeolite at elevated temperatures might not seem toosurprising, it must be pointed out that the olefins formed do notnecessarily conform to the carbon configuration of the reactant. Theolefin may and often does have a longer carbon to carbon chain than didthe reacting moiety from which it was derived, usually multiples of thereactant carbon chain length. It is even more surprising that one canproduce olefins such as ethylene and propylene from methyl ethers,particularly dimethyl ether, that is effectively a one carbon atomreactant.

According to this invention, aromatics are produced from lower aliphaticethers to about 500 to l000F, 0 to 3000 psig and 0.5 to 50 WHSV. Olefinproduction seems to predominate under less severe conditions, such asreduced contact times brought about by operating at space velocitiesgreater than about 50 WHSV. Suitable exemplary reactants includedimethyl ether, diethyl ether, methyl ethyl ether, methyl vinyl ether,ispropyl ether, n-butyl methyl ether, di-n-hexyl ether, methyl-Z-ethylhexyl ether, cyclohexyl methyl ether, etc.

It is within the scope of the invention to convert the ether compoundsfed as individuals or as admixtures of normal chemical purity. It isalso within the scope of this invention to feed such ether reactants inadmixture with other, non-ether materials such as alcohols or carbonylcompounds. These other feed materials may be reactive or inert under theconditions of this process. Their presence or absence is not a part ofthis invention. Thus, for example, it is the subject of concurrentlyfiled patent applications of different inventors to convert carbonylcontaining compounds and/or alcohols to more complex compounds undersubstantially the same conditions as are set forth'herein. Theco-feeding and co-reaction of the feeds, or one of them, set forth insaid other patent application with the feeds of this application,including possible interaction of these feeds and/or intermediatesproduced therefrom is not considered to be outside the scope of eitherthis or that patent application. Rather, such is considered to be withinthe scope of each respective application as to that portion of the feedrelated to that application.

It is generally believed by those knowledgeable in the crystallinezeolite art that contact of a zeolite with steam is deleterious to thecatalytic properties thereof and that increase in pressure temperatureand/or time of contact increases the adverse effects on the catalyst.While certain types of zeolites, notably ZSM-5 type, are substantiallymore steam stable than other zeolites, it has been found to be possibleto reduce or eliminate the hydrocarbon aromatization catalytic activity.Aromatization of aliphatic hydrocarbons as described in application Ser.No. 253,942 filed May 17, 1972, now US. Pat. No. 3,756,942 has beenattempted using this type of catalyst which had been previously severelysteam treated. It was found to be substantially impossible to aromatizeparaffmic hydrocarbons as set forth in such application with suchsteamed catalyst. It is of interest to note, however, that such steamedcatalyst is still quite active for aromatizing ether reactants. Anadditional unexpected aspect of this invention resides in the discoverythat, although it is usual and common for conversion reactions carriedout in the presence of and in contact with zeolite catalysts in generalto form coke and deposit such on the zeolite catalyst whereby graduallydeactivating the catalyst, the coke make deposited on the catalyst ofthis invention in the process of this invention is exceedingly small,much smaller than that encountered when subjecting correspondinghydrocarbon feeds to the same conversion conditions.

It is interesting to note that while aromatization of hydrocarbons, evenunsaturated hydrocarbons, is initiated to a meaningful extent at about650F and is maximized from a commercially desirable product distributionpoint of view at about 1000F, aromatization of lower ethers to generallythe same commercially acceptable product distribution initiates at about500F and is maximized at about 700F. Contacting aliphatic hydrocarbonswith this type of aluminosilicate zeolites in the same temperature andother operating condition ranges as set forth above according to thisinvention does not induce significant production of new aromatic ringsbut more usually tends to alkylate preformed, cofed aromatic ringmoieties. In this regard it should be understood that there is not aclear line of demarcation between operating conditions which inducealkylation as opposed to aromatization of fed aliphatic hydrocarbonsaccording to previously described processes. Similarly, there is not aclear line of demarcation in product distribution as a function oftemperature in the process of this invention. It can be said in generalthat lower temperatures favor olefin formation and higher temperatures,which are still generally lower than hydrocarbon aromatizationtemperatures, favor aromatization.

The following Examples are illustrative of this invention without beinglimiting on the scope thereof. Parts and percentages are by weightunless expressly stated to be the contrary.

EXAMPLES 1-4 TABLE Example No. l 2 3 4 Hydrocarbon Product DistributionCf 40.94 28.84 26.40 25.44 C; Aliphatic 17.62 33.83 37.18 35.12 C,;*Aromatics 41.44 37.33 36.42 39.38

The process of this invention can be carried out in rather conventionalup-flow or down-flow reactors packed with ZSM-5 type of aluminosilicatezeolite catalyst. The zeolite catalyst suitably occupies about 1 to 100%of the reaction zone volume and may be used in a fixed or fluidized bedarrangement. Suitable heating and/or cooling means may be employedaccording to conventional reaction zone temperature profiling design.The catalyst is suitably of a particle size of about 4 to 325 mesh.

EXAMPLE 5 This examples illustrates the conversion of dimethyl ether to(predominantly) olefins.

WHSV 1.26 Catalyst 65% H-ZSM-5/35% A1 (1/16" extrudate) Conversion 100%Hydrocarbon Product Distribution C 49.18 Aliphatic C 13.12 Aromatics Cg37.70

EXAMPLE 7 Tetrahydrofluran 1 atm. WHSV 1.39

Catalyst 65% H ZSM-5/35% A1 0 (1/16" extrudate) Conversion 99.3%

Hydrocarbon Product Distribution C; 27.41 Aliphatic C 6.43 Aromatic v C66.16

EXAMPLE 8 CH O CH O CH (methylal) P 1 atm. WHSV 1.35

Catalyst 65% H ZSM 5/35% Al O;,( l/l6" extrudate) Conversion H drocarbonProduct Distribution What is claimed is:

1. A process for converting aliphatic ethers containing a hydrocarbonconstituent which comprises contacting at least one aliphatic ether witha crystalline aluminosilicate zeolite having a silica to alumina ratioof at least about 12 and a constraint index of about 1 to 12 at anelevated temperature of about 500 to about 1000F, a pressure of about 0to 3000 psig and a space velocity of about 0.5 to 1000 WHSV under suchcombination of conditions as to convert said ether to a productcomprising hydrocarbon compounds having a higher molecular weight thanthe longest hydrocarbon constituent of a respective reactant ether.

2. A process as claimed in claim 1 wherein said ether has an alkylconstituent of 1 to 8 carbon atoms.

3. A process as claimed in claim 1 wherein said ether is a mixed alkylether.

4. A process as claimed in claim 1 wherein said catalyst is H-ZSM-S.

5. A process as claimed in claim 1 carried out at least about 500F toproduce aromatic moieties of longer hydrocarbon chain length than thereactant ether.

6. A process as claimed in claim 1 wherein said ether is dimethyl ether.

7. A process as claimed in claim 1 utilizing a reactant comprisingdimethyl ether, which dimethyl ether is at least partially converted tonew aromatic ring moieties.

8. A process as claimed in claim 1 wherein said zeolite has a crystaldensity in the hydrogen form of not substantially below about 1.6 gramsper cubic centimeter.

9. A process of converting an aliphatic ether to an aromatic hydrocarbonby contacting said ether with a crystalline aluminosilicate zeolitehaving a silica to alumina ratio of at least about 12 and a constraintindex of about 1 to 12 at a temperature of about 500 to 1000F, apressure of about 0 to 3000 P516 and a space velocity of about 0.5 to1000 WHSV.

1. A PROCESS FOR CONVERTING ALIPHATIC ETHERS CONTAINING A HYDROCARBONCONSTIUUENT WHICH COMPRISES CONTACTING AT LEAST ONE ALIPHATIC ETHER WITHA CRYSTALLINE ALUMINOSILICATE ZEOLITE HAVING A SILICA TO ALUMINA RATIOOF AT LEAST ABOUT 12 AND A CONSTRAINT INDEXT OF ABOUT 1 TO 12 AT ANELEVATED TEMPERATURE OF ABOUT 500* TO ABOUT 1000*F, A PRESSURE OF ABOUT0 TO 3000 PSIG AND A SPACE VELOCITY OF ABOUT 0.5 TO 1000 WHSV UNDER SUCHCOMBINATION OF CONDITIONS AS TO CONVERT SAID ETHER TO A PRODUCTCOMPRISING HYDROCARBON COMPOUNDS HAVING A HIGHER MOLECULAR WEIGHT THANTHE LONGEST HYDROCARBON CONSTITUENT OF A RESPECTIVE REACTANT ETHER.
 2. Aprocess as claimed in claim 1 wherein said ether has an alkylconstituent of 1 to 8 carbon atoms.
 3. A process as claimed in claim 1wherein said ether is a mixed alkyl ether.
 4. A process as claimed inclaim 1 wherein said catalyst is H-ZSM-5.
 5. A process as claimed inclaim 1 carried out at least about 500*F to produce aromatic moieties oflonger hydrocarbon chain length than the reactant ether.
 6. A process asclaimed in claim 1 wherein said ether is dimethyl ether.
 7. A process asclaimed in claim 1 utilizing a reactant comprising dimethyl ether, whichdimethyl ether is at least partially converted to new aromatic ringmoieties.
 8. A process as claimed in claim 1 wherein said zeolite has acrystal density in the hydrogen form of not substantially below about1.6 grams per cubic centimeter.
 9. A process of converting an aliphaticether to an aromatic hydrocarbon by contacting said ether with acrystalline aluminosilicate zeolite having a silica to alumina ratio ofat least about 12 and a constraint index of about 1 to 12 at atemperature of about 500* to 1000*F, a pressure of about 0 to 3000 PSIGand a space velocity of about 0.5 to 1000 WHSV.